I am sorry to hear about Quick's strange behavior of chewing on the two by fours in her whelping pen.
Given her personality (very nervous and very afraid of people) I suspect her behavior is very much anxiety based. Some of her behavior may indeed be pain related.
A few days before labor and delivery she may well have had some Braxton-Hicks type contractions (uterine "practice" contractions) as her body prepared for labor. This could have made her anxious and led to her starting to chew on the wood.
When she went into labor and for the first few days after birth she likely had very high levels of oxytocin. This hormone not only leads to milk letdown and uterine involution but it has a calming effect on the bitch too. This is hormonally how mother nature ensures that the bitch cares for her pups rather than getting stressed and either refusing to feed the pups, or eating her pups.
Her return to chewing the wood is likely her way of relieving anxiety and helping her calm herself so she is a good mother, and doesn't harm her own pups. She is showing stereotypical self calming behavior. This of course isn't good for her and ideally we would find safe ways to soothe her.
That could include dimming the lights, playing "white noise" or using a fan or soft music to block outside noise.
Make sure to limit human contact.
You could also use DAP sprays, diffusors or a collar impregnated with DAP (dog appeasing pheromone). This pheromone is a synthetic analog of the pheromone that nursing bitches normally secrete and could do wonders at calming her.
It may help to feed more proteins. Studies have shown that dogs fed more protein in stressful situations are less anxious.
It may help too to force her to leave the pups for a period of exercise at least twice daily just after the pups have been fed. That will increase her positive endorphin levels, decrease pent up energy and may make her calmer.
Best of luck with your girl. She bears close watching so she doesn't get anxious enough to hurt her pups. Perhaps setting up a baby cam so you can observe without bothering her would work.